docs: def __learn_oneself(self):
          """calculate cardinality, total and average string length"""
          if not self.__parent_path or not self.__text_nodes:
              raise Exception("This error occurred because the step constructor\
                              had insufficient textnodes or it had empty string\
                              for its parent xpath")
          # Iterate through text nodes and sum up text length
          # TODO: consider naming this child_count or cardinality
          # or branch_cnt
          self.tnodes_cnt = len(self.__text_nodes)
          # consider naming this total
          self.ttl_strlen = sum([len(tnode) for tnode in self.__text_nodes])
          # consider naming this average
          self.avg_strlen = self.ttl_strlen/self.tnodes_cnt